1. Field of the Invention
The present invention pertains to a ball end mill having at least one cutter insert releasably attached to an end mill body thereof.
2. Prior Art
FIGS. 1 to 3 show one conventional ball end mill as disclosed in Published Examined Japanese patent application No. 59-21725. The end mill comprises a generally cylindrical end mill body 100 and an indexable cutter insert 102 releasably attached to a forward end of the end mill body 100. The insert 102 comprises a plate defined by a front face 104, a rear face 106 and a side periphery lying between the front and rear faces 104 and 106. A pair of opposite notches 108 of a generally V-shape are formed in the side periphery to interrupt the side periphery to provide a pair of opposite side faces 110. Each of the V-shaped notches 108 extends from the front face 104 to the rear face 106 and is defined by a pair of first and second opposed walls 112 and 114. The first wall 112 is flat and perpendicular to the front face 104 while the second wall 114 is convexly curved when viewed in a direction perpendicular to the first wall 112. Each of the side faces 110 assumes a generally quadrantal shape when viewed in a direction perpendicular to the front face 104, and cooperates with the front face 104 and the curved second wall 114 of the notch 108 to define a cutting edge 116 which is convexly arcuate as viewed in the same direction. One of the cutting edges 116 of the insert 102 is indexed in a working position to extend outwardly beyond the front end and outer periphery of the end mill body 100, and the leading end portion 116a of the indexed cutting edge 116 disposed adjacent to an axis O of the end mill body 100 is convexly curved when viewed axially of the end mill body 100.
In the ball end mill described above, the leading end portion 116a of the indexed cutting edge 116 begins to engage a workpiece first, and then other portions of the cutting edge 116 begin to engage the workpiece as the end mill body 100 rotates. Accordingly, the cutting load increases gradually as the cutting operation proceeds, and a great load will not be exerted on the indexed cutting edge 116 at a time, so that the cutting edge 116 is less liable to damage.
In such a prior art ball end mill, however, the flat wall 112 of the V-shaped notch 108 prevents a smooth discharge of chips during the cutting operation and causes the jamming of chips.